A poppet valve having a cooling medium metal stored therein tends to be used in an internal-combustion engine so as to reduce a thermal load. When the cooling medium metal is stored into the poppet valve, a poppet valve intermediate is prepared that has an internal space having an opening on one axial end side, and is arranged with the opening on one axial end side facing upward and, after the inert gas is filled into the internal space of the poppet valve intermediate, the cooling medium metal is supplied from the opening on one axial end side of the poppet valve intermediate before the opening on one axial end side of the poppet valve intermediate is closed. As a result, not only can the cooling medium metal be stored inside (in the internal space) of the poppet valve, the cooling medium metal can be prevented from being oxidized by an air initially present in the internal space of the poppet valve intermediate, so as to enable the cooling medium metal to produce original heat transfer performance thereof.
In a proposed method of filling an inert gas into the internal space of the poppet valve intermediate, as described in Patent Document 1, a poppet valve intermediate is arranged such that an opening on one axial end side thereof faces upward with a nozzle inserted into near the bottom part of the internal space of the poppet valve intermediate, and the nozzle is moved upward while an inert gas is ejected from the nozzle. According to this method, as the nozzle moves upward, the inert gas is supplied into the internal space of the poppet valve intermediate continuously from the lower side thereof and, when the nozzle is moved outside the internal space of the poppet valve intermediate, the internal space of the poppet valve intermediate is entirely filled with the inert gas in place of the original air.